Conventional drill stem tester valves, safety valves and other service tools utilize tension sleeves or shear pins to initiate some function of the tool. With safety joints, for example, the tension sleeve or shear pins must be parted or sheared to allow further string manipulation which facilitates further operation and/or disconnection of the safety joint.
There are a number of disadvantages associated with such conventional designs. First, as wells get deeper and the workstrings heavier, it is becoming increasingly difficult to select a tension sleeve for each specific job. Generally, it is desirable to have a high value for the tension sleeve to avoid accidental operation. Some sizes of safety joints only have two choices for the tension sleeve, for example, 40,000 lbs. or 60,000 lbs. However, a long heavy workstring may not tolerate a very high value tension sleeve because the tensile rating of the workstring could be exceeded. Second, installing 60 or more shear pins in a shear set can be very time consuming, as is generally the case with conventional designs. Third, once sheared, the shear pins parts are dropped in the well which may render fishing operations more difficult.
Accordingly, there is a need in the art for a retaining mechanism for use with a pressure responsive downhole tool which alleviates and/or overcomes these prior art disadvantages, thus providing a safer, adjustable, and more reliable downhole tool.